I don't know what to do about my sex?

Hi I'm 20 years old and have always really had a big problem getting hard for sex...I tried to have sex when I was 14 and I couldn't get hard...I tried again when I was 15 and still couldn't...I became very self conscious of this and terribly imbarrased that I didn't try again untill I was almost 18...When I tried at about 18 I was able to get hard and I was so ecstatic I was able to have sex with this girl every time we tried and I thought I had broke the curse but when we recently split up I tried to have sex with another girl for the first time and again I couldn't get hard...frustrated imbarrased and upset I still gave it yet another try and I got the same result...I wasn't able to get hard...please give me any advice or information you might have regarding this situation...thank you very much